This invention relates to a manual pushbutton keyboard system for an electronic pocket calculator, a remote TV tuner, a pushbutton telephone, or for other electrical or electronic appliances, and it is particularly concerned with such a keyboard which utilizes dished or domed discs as switch actuating elements of single-throw (ST) momentary switches for the keyboard.
More generally, calculator keyboards conventionally include a plurality of ST momentary switches and a network of conductor paths on a printed circuit board leading to terminals at one margin of the board for connection of the keyboard switches to other electronic components, such as to various solid state, integrated circuit, and semi-conductor logic components within a calculator. Prior art keyboards, such as shown in the coassigned U.S. Pat. Nos. 3,684,842; 3,806,673 and 3,808,384, utilized domed discs as switch actuating elements. Use of such doomed discs is desirable for various reasons including the tactile feedback the disc gives the operator when the disc suddenly moves from an unactuated position to an actuated position. As disclosed in the last two mentioned patents such discs are utilized with both single and multipole switches and generally comprise an electrically conductive disc supported at or near its outer margins by an outer contact. Since the disc is formed with a concave configuration in its unactuated condition (facing the contacts) it is held out of touch with one or more inner contacts disposed beneath the disc. As the disc is actuated by an operator depressing a key the configuration of the disc changes with the center moving to or below the plane formed by its outer periphery until the disc touches the inner contacts thereby establishing a circuit between the outer and inner contacts through the disc. Although this approach is effective with the plurality of poles of a given switching station being energized at essentially the same moment, there are certain applications in which it is desirable to preclude the possibility of one pole being energized slightly before another one at the same switching station.